The structural and functional alterations of vascular endothelium caused by fluid shear stress are being investigated using cultured endothelial cells and a new in vitro apparatus for producing controlled fluid shear stress. The apparatus incorporates a shallow cone rotating above a flat plate; shear stresses between 10 to the minus 2nd power and 200 dynes/sq. cm. can be produced; both laminar and turbulent flow will be investigated. Specific parameters of endothelial structure and function to be measured under varying conditions of shear include: growth patterns and growth kinetics; migration and mitosis following injury; cell orientation and morphology; rates and mechanisms of endocytosis; prostaglandin (PGI2) metabolism; and other indices of endothelial metabolism (activities of angiotensin-I converting enzyme and histidine decarboxylase).